The analysis of particular lethal mutations has demonstrated the existence of neoplasms in Drosophila melanogaster (Gateff, 1978b). The availability of temperature sensitive mutations provides a system in which the initiation of the neoplasm can be controlled and the consequences analyzed. We have isolated and begun the characterization of temperature sensitive alleles at two neoplastic loci, Tum1 and 1(2)gl. The Tum1 mutation develops a neoplasm of the larval lymph gland (Hanratty and Ryerse, 1980) and the 1(2)g1ts mutation develops a neoplasm of the wing imaginal disc. The proposed research on the Tum1 mutation will involve the analysis of the recruitment of host tissue into the developing neoplasm, the effect of the developmental stage on the competance of Tum1 lymph glands to undergo neoplastic development and the effect of parasitism on the expression of the neoplasm. The proposed research on the 1(2)g1ts mutation involves defining: (1) the effect of injury and the initiation of epimorphic regulation on the initiation of the neoplasm, (2) the effect on neoplastic development on the developmental competance and histology of the wing disc tissue, (3) the consequences of neoplastic development on tissue regulation, growth kinetics, and the pattern of proteins synthesized by wing disc tissue.